Actuation of a robotic element is optimally provided by an actuator that is light weight and low cost and that exhibits capabilities of high power and force or torque generation, shock tolerance, and above all, precise force control and force control stability. Actuators that are overly bulky or heavy put a strain on the other elements of the system within which they reside; the remaining actuators in the system must accommodate the weight with additional power. As robotic and automated systems continue to increase in size, complexity and functionality, the number of system components so too increases, resulting in the need for economically-priced system parts.
In addition, as the modes of interaction between robotic systems and their environments increase in freedom and complexity, high power, high force or torque generation is required to provide capabilities in a wide range of robotic load manipulation tasks. But at the same time, however, the force or torque generation must be precisely controlled to enable interaction with the robot's environment without causing damage to either the environment or the robot. Indeed, shock tolerance is required of robotic actuator systems because the chance of unexpected or unpredictable high-force interactions with task and load manipulation environments is greatly increased in such complex applications.
Heretofore these actuator attributes have been in contradiction. For example, to achieve a decrease in actuator weight, gears are conventionally introduced in an actuator employing a motor. Although a gear train does lighten the system by allowing for use of a smaller motor operating at higher speeds, it also sensitizes the system to shock loads; shock-induced damage of gear trains is known to be one of the most common modes of actuator failure. In an effort to enhance gear train strength to reduce gear damage, precise materials and designs are often employed for gear systems. Typically such systems are prohibitively expensive and therefore are not acceptable for common robotic actuation applications. As a result, design efforts toward a strong, inexpensive, light weight, shock resistant actuator that provides precise force control have been suboptimal.